Watermarking is a common technique to mark the data processed by a receiving device. It is a way to trace the content if the latter is found on Internet for example, without protection.
Various solutions exist to embed a watermark in an audio/video content once said audio/video content is descrambled. A first approach is to embed the watermark at the emission side. This is described in the document EP 2 204 979. The server fingerprints the data and the receiver can extract this fingerprint for authentication. Another approach is the one proposed by the document US 2010/0040228 in which once the video stream is descrambled, the receiving device add a mark specific to an identification of the receiving device.
A receiving device has, for example, the form of a set-top-box, an advance television or a CAM (conditional access module) in charge of receiving the audio/video stream and removing the protection layer. For that purpose, the receiving device comprises at least a descrambler (which receives a key) and a decoder. The decoder is in charge of transforming the compressed format of the audio/video stream into a format suitable for the display device.
The receiving device can also comprise a watermarking module which watermarks the data outputted from the descrambler module or the audio/video decoder, this watermark being parameterized by an internal parameter of the receiving device.
The receiving device comprises generally a security module to handle all the security operations. A security module can be a removable module such as a smartcard or a USB dongle, or embedded in the receiving device in the form of a single chip mounted on the circuit board or a mixed of them